Plywood panels are formed from a plurality of layers of wood veneer disposed in face-to-face relationship with the grain on alternate layers extending in generally othogonal directions. In the prior art, the veneer generally is peeled from a log, dried and then prepared to eliminate defects such as knots, knot holes and the like. The prepared veneer layers then are laid up in face-to-face relationship with appropriate adhesives disposed therebetween. These veneer layers are then urged toward one another under appropriate conditions of heat and pressure to form a substantially integral plywood panel structure. The panel then may be cut into smaller panels of appropriate size, and any remaining defects may be routed and patched. The panel then may be sanded and subjected to a quality control inspection. Panels that are still deemed defective may be returned to the routing and patching stations or to the sanding station to assure that necessary quality control is achieved. The completed panels then are appropriately packaged and shipped.
In the past, the preparation of veneer sheets and the routing and patching on completed panels have been carried out manually based upon the visual perceptions of inspectors. Typically the defects in the veneer sheets used in the plywood panel have been corrected by stamping, routing or otherwise removing generally boat-shaped portions of preselected and uniform sizes from the veneer sheet at substantially the location of an observed defect. Specifically, the inspector could manually remove the observed defects by cutting uniform boat-shaped apertures in the veneer, or the inspector could direct an automated stamping or routing apparatus to the respective locations of the defects to effect the formation of boat-shaped apertures therein. Boat-shaped wooden patches then were inserted in the formed apertures.
There are several reasons for forming uniform and substantially identical apertures in the defective plywood sheets regardless of the specific size or shape of the defect. For example, the formation of uniform apertures in the veneer sheet of the prior art avoids the need to manually or visually inspect and measure the size of defects. Second, all patches are identical, and there is no need to match the patch to the particular defect, size and shape. Finally, it has been observed that if wooden patches are to be used, there are operational and performance advantages to using patches having a boat or oval shape. Specifically, the respective grains of the wooden patch and the veneer sheet can be made to match more closely. In certain instances, circular or diamond shaped patches have been used.
Several examples of patching veneer sheets during the formation of plywood are shown in U.S. Pat. No. 2,336,703, U.S. Pat. No. 2,454,016, U.S. Pat. No. 2,536,665 and U.S. Pat. No. 2,583,396 all of which issued to P. F. Skoog. Still other such patches and methods of patching are shown in U.S. Pat. No. 1,689,705 to F. L. Walker, U.S. Pat. No. 2,649,876 to W. F. Thompson et al, U.S. Pat. No. 2,674,770 to E. V. Bennett et al, U.S. Pat. No. 2,675,038, to Carlson and U.S. Pat. No. 3,616,117 to Anderson et al.
Forsythe et al shown in U.S. Pat. No. 3,741,853 and U.S. Pat. No. 3,844,863 that defects in laid up panels can be routed out, and the resulting hole in the panel can be filled with a filler composition having a flowable liquid consistency. The filler of the Forsythe et al references includes a mixture of cork particles and resin, wherein the cork particles stratify to the uppermost region and can readily be sanded or otherwise finished.
Prior art plywood panels often are graded with the particular grade signifying the range of possible end pieces that may be available. For example, plywood panels having no defects on the outer layer usually are classified as grade A indicating that the panel may be finished with a transparent or semi-transparent coating and used in furniture, cabinets, wall panels or other structures where the panel is unpainted, visible and necessarily of high aesthetic quality. Grade B usually denotes panels that require a smooth finish but that will be painted or otherwise coated with an opaque medium. Grade B panels may include a plurality of the above described boat-shaped patches or fillers provided the surface of the panel is smooth and the perimeters of the patches are not readily observable. Grade C may define panels that are not properly patched and therefore are usable only in situations where the panel will not readily be observed.
The above described patching techniques have several deficiencies. For example, the entire prior art patching procedure has relied extensively on visual observations and manual defect removal, or at least manual control of an apparatus for removing defects. In this respect, the prior art patching process has been subjected to human failures and has required a relatively high labor intensity. For example, a typical plywood production line may include five people to perform routing/patching operations. Furthermore, the prior art patches, such as those shown in the above identified Skoog Patent references, have negatively affected the quality of the resulting panels. Thus, a panel having the widely used boat shaped patches can never achieve the A grade described above. On the other hand, the known patching techniques such as those shown in the Forsythe et. al. patents identified above have added even more to manufacturing time and cost.
In view of the above, it is an object of the subject invention to provide an apparatus and method for providing plywood panels of improved quality.
It is another object of the subject invention to more efficiently remove and patch defects in the outer veneer layers of plywood panels.
It is an additional object of the subject invention to provide a method and apparatus for providing plywood panel patches that substantially conform to the shape of the original defect in the panel.
It is a further object of the subject invention to provide a method and apparatus for automatically detecting defects in a plywood panel, removing the detected defects and providing a patch of the appropriate size.
It is still another object of the subject invention to provide an improved quality plywood panel that is substantially free of observable defects or observable patches.